1. Field of the Invention
This invention relates to a metering valve and more particularly, to a metering valve utilizing a metered amount of a fluid or compressed gas carrier combined in a mixing chamber with a metered amount of a medicament and the like. The ingredients are measured and transported by a dosing means under conditions whereby a gaseous medicament dispersion is formed.
2. Description of the Prior Art
Metered dose inhalers (MDIs first introduced in 1956) are self-contained packages usually consisting of an aluminum can and a lid with a metering valve crimped on it. The formulation inside the can usually consists of propellant(s) and drugs, either in solution or suspension, along with excipients to aid in stability and dosimetry of the product. The valve system is fitted to an actuator along with a mouthpiece, which links the canister to the patients"" mouth. When the valve is actuated a pre-metered volume of the formulation is released through the valve into the mouthpiece. The latent heat of vaporization of the volatile propellant provides the energy for atomization of droplets of product released from the valve. Usually, a partial evaporation of about 10-20% of propellant vehicle occurs immediately after expulsion of product from the nozzle. It is this violent evaporation of propellant that causes instant break-up of aerosol droplets into fine respirable particles, usually xe2x89xa610 xcexcm subsequently yielding particles with a mass median aerodynamic diameter (MMAD) in the range between 3 and 8 xcexcm.
Chloroflurocarbons (CFCs) are substituted halogenated alkanes used extensively in the pharmaceutical industry because they are inert, non-toxic and possess enough vapor pressure to warrant their use as drug delivery carriers in pharmaceutical aerosols. Aerosolized beta-agonists and anti-allergic compounds were the first series of pharmaceuticals to use CFCs as propellants for drug delivery to the lung. For these products, appropriate combinations of CFC propellant blends are necessary to insure a proper balance between vapor pressure and device performance. Such propellant combinations enable the formation of a fine spray upon actuation of the delivery mechanism. The use of a metering valve allows delivery of a predetermined volume of the product upon actuation. Hence, these delivery systems are also referred to as metered-dose inhalers (MDIs). These CFC propellants are suggested to interfere with stratospheric ozone protection. In 1991, the total consumption of CFCs in medical aerosols was estimated to be about 0.5% of the total worldwide consumption of these materials, but despite such low levels of CFCs consumed in MDIs, environmentally conscious groups are committed to see a total ban on the production and use of these products. There are medical, ethical and social consequences for abandoning CFCs totally before suitable alternatives are available.
The need to replace CFCs in clinical and industrial applications based on scientific, medical and environmental mandates, including the Montreal Protocol, has led to large research programs to identify and test acceptable substitutes. A number of possible alternative propellants have been rejected for safety reasons. Some, for example compressed gases, simply do not have the physical properties needed to achieve uniform doses from MDIs. Others, for example hydrocarbons, are unsuitable because of their flammability. Yet others are toxic because they cause drowsiness or affect the heart. Attention is now being focussed on two hydrofluoroalkanes (HFAs), HFA-134a and HFA-227, respectively called tetrafluorethane and heptafluoropropane. These propellants appear to have the necessary physical properties, do not cause ozone depletion, are non-flammable and, most importantly, appear to be non-toxic when compared to CFCs at equivalent doses. Establishing the suitability of these alternative propellants before introducing them for use in MDIs involves a lengthy and highly regulated process. The significant progress made thus far is a reflection of the substantial development effort made by the pharmaceutical industry to phase out CFCs from MDIs while maintaining the range of treatment options available for patients.
Although HFAs possess several desirable properties which make them suitable, effective and safe alternatives to CFC propellants, they nonetheless are greenhouse gases and have the potential to cause undue global warming (e.g., warming of oceans, and water evaporation, which would further delay the transmission of heat). Thus, future drug delivery systems should concentrate on technology platforms that are truly inert to the environment.
More recently, electronically-controlled devices which use aqueous formulations in a manner similar to conventional MDIs have been developed. Piezo devices produce a spray out of a single drop of drug solution. The drug is metered by a nozzle onto a mesh or grid. The device usually consists of an actuator head, a housing, a piezo-electric element, and a mesh. The liquid droplet on the mesh is energized by the piezo-electric element using an alternating voltage thus causing vibrations of drug molecules in the droplet. The vibrations are amplified by the housing. This causes the mesh and the liquid droplet to also vibrate subsequently resulting in spray formation. Particle size thus depends on the flow rate of drug solution onto the mesh. Particle size distribution of the aerosolized particles depend also on the hole size in mesh, number of holes in the mesh, and magnitude of the vibrational energy.
Nebulized inhalation systems are aqueous formations which are aerosolized with the aid of external energy. The process converts water droplets to the vapor phase, which is inhaled by the patient. Unlike MDIs, the composition of these systems resembles injectable formulations and is administered with specific devices, namely compressors and atomizers. The formulations generally contain dissolved drug but suspensions of the drug together with other inactive excipients may be neubulized for stability and taste reasons. At the time of use, the solution is poured into the nebulizer, which generally contains an ultrasonic probe or an air jet source to aid aerosolization. A mouthpiece or hood traps the resulting particles so that tidal breathing may be used by the patient to inhale the drug. Nebulizers are not compact like MDIs and they are often too bulky for ambulatory use. In addition, they take several minutes to hours to complete the dosing. In spite of this limitation, nebulizers offer several significant advantages. They contain mainly water as a vehicle and therefore present no great safety concerns in regard to formulation toxicity.
Nebulizers present a variety of dosing schemes and dose volumes so that they are flexibly adaptable for drugs whose activity is so low as to require several milligram to gram quantities to obtain measurable pharmacologic effects. However, there are a number of technical and clinical limitations concerning nebulized drug technologies. Sterility of drug formulations, the need for ancillary hardware, example generator, and their suitability to non-ambulatory care because of size, places them at a disadvantage.
Unlike MDIs and nebulizers, where drug solution or suspension is initially released as a xe2x80x9cwetxe2x80x9d spray, DPIs constitute formulations and devices where a predetermined dose of active, either alone or in a blend with some carrier like lactose, is released as a fine mist of dry powder for inhalation. These systems differ significantly from MDIs and nebulizers in that they do not contain any liquid media (e.g., propellant or water). The drug is formulated in a manner so that it readily disperses into particles of respirable size range (i.e. xe2x89xa610 xcexcm). The powder dispersion is initiated either by inspiration or by some external source, e.g., an electronic vibrator included with the device hardware. In older DPI technologies, the formulation to be inhaled was packaged in single dose units, for example in hard gelatin capsules. The unit dose capsules were manually placed into the device. After breakage of the shell immediately prior to use, the dose was inhaled through a grid placed in the path of the powder. Newer DPI devices are reservoir systems capable of providing multiple dosing without a manual transfer of dosing units into the device.
Prior art includes U.S. Pat. No. 5,839,622 to Bicknell et al.; U.S. Pat. No. 5,641,096 to Robbins et al.; U.S. Pat. No. 5,568,884 to Bruna; U.S. Pat. No. 5,490,615 to Robbins et al.; U.S. Pat. No. 5,437,999 to Poss et al.; U.S. Pat. No. 5,082,148 to Dunning; U.S. Pat. No. 3,731,851 to Rauh; and U.S. Pat. No. 3,416,709 to Shultz et al.
It is therefore an object of the present invention to provide a powder/liquid metering valve which reliably and consistently delivers the desired dose of dry or liquid medicament to a user in a reasonably short period of time.
It is therefore a further object of the invention to provide a powder/liquid metering valve which is reproducibly filled with medicament during the life of the product.
It is therefore a still further object of the present invention to provide a powder/liquid metering valve that uses a propellant that is inert, non-flammable and non-toxic.
It is therefore a still further object of the present invention to provide a powder/liquid metering valve that uses a propellant which does not raise significant environmental concerns.
It is therefore a still further object of the present invention to provide a powder/liquid metering valve combined with a metered dose inhaler to be portable in size.
It is therefore a still further object of the present invention to provide a powder/liquid metering valve for a metered dose inhaler which has an operation substantially identical to that of current CFC/HFA based systems.
These and other objects are attained by providing a powder/liquid metering valve which includes two functioning metering elements that work in a synchronized manner with each other to dispense precise quantities of a gas phase and a medicament or other material from separate chambers/reservoirs. The first element being a gas metering spindle with an appropriately designed helix profile that when rotated partially or fully along its long axis when positioned against a sealing element it serves to throttle an appropriate liquefied or compressed gas through a mixing chamber and eventually out through an orifice in the mixing chamber positioned perpendicular to the entry point of spindle. Coincident with the movement of the gas metering spindle or shortly thereafter a second spindle element, a drug or material metering spindle, is designed with an appropriate helix profile such that when it is in contact with a reservoir of active ingredient, in the form of a dry powder, solution or suspension, the rotational movement of the drug metering spindle carries forward a precise metered quantity of material contained in the reservoir and presents the material to the mixing chamber simultaneously or with a delay versus the presentation of the expanding gas. The rotation of the drug metering spindle in association with its sealing element will ensure only the precise desired quantity of material is metered out. The helical profile of the drug metering spindle is designed such that with pressure applied by the user and the subsequent rotation of the spindle, the drug metering spindle can throttle material into and out of the mixing chamber before during and after the material is presented to the mixing chamber. The sequencing of the presentation of materials from the gas metering and drug metering spindles serves to create a negative pressure at the interface of the spindles at the start of the metering process followed by a full mixing of the material in the gas stream including deagglomeration and particle/droplet size formation and finally a cleansing of the drug metering spindle prior to its return to its at rest position.
The orientation of the entry of material from the gas metering and drug metering spindle into the mixing chamber is parallel to the long axis of each spindle. The drug reservoir may include a collapsible bellow or other means suitable for the purpose of maintaining a constant pressure on the medicament provided to the metering element. The exit orifice port may be perpendicular or parallel to the long axis of the spindles.